Add method read_bits_int_le

See kaitai-io/kaitai_struct#155

Author: generalmimon

kaitaistruct.py

@@ -221,7 +221,7 @@ def align_to_byte(self):
         self.bits = 0
         self.bits_left = 0
 
-    def read_bits_int(self, n):
+    def read_bits_int_be(self, n):
         bits_needed = n - self.bits_left
         if bits_needed > 0:
             # 1 bit  => 1 byte
@@ -230,11 +230,7 @@ def read_bits_int(self, n):
             bytes_needed = ((bits_needed - 1) // 8) + 1
             buf = self.read_bytes(bytes_needed)
             for byte in buf:
-                # Python 2 will get "byte" as one-character str, thus
-                # we need to convert it to integer manually; Python 3
-                # is fine as is.
-                if isinstance(byte, str):
-                    byte = ord(byte)
+                byte = KaitaiStream.int_from_byte(byte)
                 self.bits <<= 8
                 self.bits |= byte
                 self.bits_left += 8
@@ -253,6 +249,34 @@ def read_bits_int(self, n):
 
         return res
 
+    # Unused since Kaitai Struct Compiler v0.9+ - compatibility with
+    # older versions.
+    def read_bits_int(self, n):
+        return self.read_bits_int_be(n)
+
+    def read_bits_int_le(self, n):
+        bits_needed = n - self.bits_left
+        if bits_needed > 0:
+            # 1 bit  => 1 byte
+            # 8 bits => 1 byte
+            # 9 bits => 2 bytes
+            bytes_needed = ((bits_needed - 1) // 8) + 1
+            buf = self.read_bytes(bytes_needed)
+            for byte in buf:
+                byte = KaitaiStream.int_from_byte(byte)
+                self.bits |= (byte << self.bits_left)
+                self.bits_left += 8
+
+        # raw mask with required number of 1s, starting from lowest bit
+        mask = (1 << n) - 1
+        # derive reading result
+        res = self.bits & mask
+        # remove bottom bits that we've just read by shifting
+        self.bits >>= n
+        self.bits_left -= n
+
+        return res
+
     # ========================================================================
     # Byte arrays
     # ========================================================================